arsenic removal from groundwater by fe-mn oxidation and microfiltration

112 Pages·2005·0.82 MB·English

by  Sevil Caniyilmaz

ARSENIC REMOVAL FROM GROUNDWATER BY FE-MN OXIDATION AND
MICROFILTRATION

by

Sevil Caniyilmaz

B.S., Middle East Technical University, 2003

Submitted to the Graduate Faculty of

School of Engineering in partial fulfillment

of the requirements for the degree of

Master of Science

University of Pittsburgh

2005
UNIVERSITY OF PITTSBURGH

SCHOOL OF ENGINEERING

This thesis was presented

by

Sevil Caniyilmaz

It was defended on

November 30, 2005

and approved by

Radisav D. Vidic, Professor, Civil and Environmental Engineering Department

Ronald D. Neufeld, Professor, Civil and Environmental Engineering Department

Leonard W. Casson, Associate Professor, Civil and Environmental Engineering Department

Thesis Advisor: Radisav D. Vidic, Professor, Civil and Environmental Engineering Department

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ARSENIC REMOVAL FROM GROUNDWATER BY FE-MN OXIDATION AND
MICROFILTRATION

Sevil Caniyilmaz, MS

University of Pittsburgh, 2005

Although arsenic has been classified as human carcinogen and its acute toxicity has long been
known, the long term health effects of trace arsenic levels have only recently been realized. The
maximum contaminant level (MCL) for arsenic in drinking water was consequently lowered
from 50 µg/L to 10 µg/L in 2002, resulting in many water utilities needing upgraded to achieve
compliance. In groundwater treatment, Fe-Mn oxidation and microfiltration has been recognized
as a cost-effective technology since arsenic removal is facilitated during the removal of iron and
manganese.
This study investigated the efficiency of arsenic removal using Fe-Mn
oxidation/microfiltration under various process conditions including iron to arsenic ratio, pH,
potassium permanganate dose, contact time, oxidation state of iron, and stirring in dead-end
filtration cell.
Arsenite removal was relatively insensitive to variations in pH in the range of 6.5-8.0
when only aeration was applied, but the impact of pH was important in the potassium
permanganate oxidation. At neutral pH, iron to arsenic ratio of 60 was sufficient to reduce the
arsenic concentrations ranging from 25-250 ppb to below 10 ppb (primary MCL for arsenic) with
aeration and microfiltration. The oxidation state of iron did not considerably affect the arsenic
removal. Oxidation with potassium permanganate facilitated additional arsenite removal
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compared to aeration alone. Although higher arsenic removals were observed at pH 7.0 than at
pH 8.0, identical residual arsenic concentrations were obtained with 0.5 mg/L permanganate
dose at both pH values.
In experiments with various iron levels, concentrations of iron in the permeate remained
around 0.01 mg/L, which is far below the secondary MCL for iron (0.3 mg/L), while the
manganese standard (0.05 mg/L) was only met when initial concentration of manganese was
0.2 mg/L. Iron and manganese particles were the primary reason for membrane fouling.
The results of this study are important for water treatment systems using groundwater
with elevated arsenic and iron concentrations as a raw water source. The proposed technology is
much simpler to operate than a conventional coagulation process and chemical requirements are
minimized by utilizing existing iron concentration in the raw water.

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TABLE OF CONTENTS

ACKNOWLEDGEMENTS.........................................................................................................xiii
INTRODUCTION..........................................................................................................................1
1.0 LITERATURE REVIEW...................................................................................................3
1.1 ARSENIC IN NATURAL WATERS.............................................................................3
1.1.1 Arsenic Contamination...........................................................................................3
1.1.2 Arsenic in the Environment....................................................................................4
1.1.2.1 Sources of Arsenic..............................................................................................4
1.1.2.2 Mobility of Arsenic.............................................................................................5
1.1.2.3 Arsenic Chemistry..............................................................................................6
1.1.3 Health Impacts of Arsenic....................................................................................10
1.1.3.1 Regulations.......................................................................................................10
1.1.3.2 Toxicity.............................................................................................................11
1.2 ARSENIC REMOVAL BY CONVENTIONAL TREATMENT PROCESSES.........13
1.2.1 Coagulation Processes..........................................................................................16
1.2.2 Fe-Mn Oxidation Technology...............................................................................18
1.2.2.1 Oxidation of Iron and Manganese.....................................................................20
1.2.2.2 Oxidation of Arsenite........................................................................................21
1.2.3 Effects of Water Quality Parameters on Arsenic Removal..................................24
1.2.3.1 pH......................................................................................................................24
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1.2.3.2 Fe/As Ratio.......................................................................................................26
1.2.3.3 Initial As(III)/As(V) Concentration..................................................................27
1.3 ARSENIC REMOVAL BY MEMBRANE PROCESSES...........................................29
1.3.1 Application of Microfiltration in Water Treatment..............................................30
1.3.1.1 Membrane Fouling............................................................................................31
1.3.2 Arsenic Removal with Microfiltration..................................................................33
1.3.3 Arsenic Removal with Chemical Pretreatment Followed by Microfiltration.......34
2.0 MATERIALS AND METHODS......................................................................................38
2.1 REAGENTS AND STOCK SOLUTIONS...................................................................38
2.2 PREPARATION OF FEED WATER...........................................................................40
2.3 OXIDATION................................................................................................................40
2.3.1 Aeration.................................................................................................................41
2.3.2 Oxidation with Potassium Permanganate.............................................................41
2.4 MICROFILTRATION..................................................................................................42
2.4.1 Microfiltration Set-up...........................................................................................42
2.4.2 Membrane.............................................................................................................43
2.4.3 Filtration Procedure..............................................................................................44
2.5 WATER QUALITY ANALYSIS.................................................................................45
2.5.1 Iron and Manganese Analysis...............................................................................45
2.5.2 Arsenic Analysis...................................................................................................47
3.0 RESULTS AND DISCUSSION.......................................................................................51
3.1 THE EFFECT OF pH...................................................................................................52
3.1.1 Water Quality........................................................................................................52
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3.1.2 Permeate Flux.......................................................................................................54
3.2 THE EFFECT OF IRON TO ARSENIC RATIO.........................................................57
3.2.1 Water Quality........................................................................................................57
3.2.2 Permeate Flux.......................................................................................................63
3.3 STIRRED VERSUS UNSTIRRED DEAD-END FILTRATION CELL.....................65
3.3.1 Water Quality........................................................................................................65
3.3.2 Permeate Flux.......................................................................................................67
3.4 THE EFFECT OF CONTACT TIME FOR POTASSIUM PERMANGANATE
OXIDATION............................................................................................................................69
3.4.1 Water Quality........................................................................................................69
3.4.2 Permeate Flux.......................................................................................................72
3.5 THE EFFECT OF POTASSIUM PERMANGANATE DOSE AND pH....................73
3.5.1 Water Quality........................................................................................................73
3.5.2 Permeate Flux.......................................................................................................81
3.6 THE EFFECT OF OXIDATION STATE OF IRON...................................................84
3.6.1 Water Quality........................................................................................................84
3.6.2 Permeate Flux.......................................................................................................86
4.0 SUMMARY AND CONCLUSIONS...............................................................................89
5.0 RECOMMENDATIONS FOR FUTURE STUDIES.......................................................93
BIBLIOGRAPHY.........................................................................................................................95

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LIST OF TABLES

Table 1 Best Available Technologies (BATs) and their arsenic removal efficiency. Percent
removal figures are for arsenate removal [Wickramansinghe et al., 2004]................14

Table 2 Technical specification of Supor®200 membrane disc filter [Pall Co. website]........44

Table 3 Furnace heating program............................................................................................49

Table 4 The effect of pH on the permeate quality for artificial groundwater with initial Fe(II),
Mn(II) and As(III) concentrations of 5 mg/L, 1 mg/L and 50 ppb, respectively. Only
aeration was applied for the oxidation of the contaminants.......................................52

Table 5 Permeate quality data of artificial groundwater prepared with different iron to arsenic
ratios and 1 mg/L manganese at neutral pH. Only aeration was applied....................59

Table 6 The effect of unstirred and stirred dead-end cell filtration systems on the permeate
quality for artificial groundwater with initial arsenite of 150 ppb, manganous ion of 1
mg/L and ferrous ion of 1, 5, and 10 mg/L at neutral pH. Only aeration was applied.
.....................................................................................................................................66

Table 7 The effect of contact time provided after potassium permanganate addition on the
permeate quality for artificial groundwater with initial ferrous and manganous ions of
1 mg/L and arsenite of 50, 100, and 150 ppb at neutral pH........................................70

Table 8 The effect of potassium permanganate dose on the permeate quality for artificial
groundwater with initial ferrous ion of 1 mg/L, manganous ion of 1 mg/L and arsenite
of 50, 100, and 150 ppb at pH 7.0...............................................................................74

Table 9 The effect of pH and potassium permanganate dose on the permeate quality for
artificial groundwater with initial ferrous ion of 1 mg/L, manganous ion of 1 mg/L
and arsenite of 50 ppb.................................................................................................77

Table 10 The permate quality data for artificial groundwater with initial ferrous ion of 1 mg/L,
manganous ion of 0.2 mg/L and arsenite of 50 ppb obtained after aeration alone and
aeration followed by potassium permanganate oxidation at pH 8.0...........................80

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Table 11 The effect of oxidation state of iron on the permeate quality for artificial groundwater
with initial concentrations of manganous ion of 1 mg/L, arsenite of 100 ppb and
various concentrations of iron at pH 7.0. Only aeration was applied for the oxidation
of the contaminants.....................................................................................................85

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LIST OF FIGURES

Figure 1 The global arsenic cycle [Shih, 2005]............................................................................6

Figure 2 The Eh-pH diagram for arsenic at 25 °C and 1 atm, with total arsenic 10-5 mol/L and
total sulfur 10-3 mol/L; solid species are indicated in parentheses in crosshatched area
[Shih, 2005]...................................................................................................................8

Figure 3 Ferric hydroxide speciation (the species are Fe(OH) +, Fe(OH) and Fe(OH) -,
2 3 4
respectively) [Chwirka et al., 2004]............................................................................25

Figure 4 Pressure Driven Membrane Process Classification [EPA, 2000].................................30

Figure 5 Schematic representation of microfiltration [Bruggen et al., 2003].............................31

Figure 6 Aeration of the feed water............................................................................................41

Figure 7 The experimental set-up of dead-end cell system........................................................43

Figure 8 Perkin-Elmer model 1100B atomic absorption spectrophotometer used for the analysis
of iron and manganese................................................................................................46

Figure 9 Absorbance as a function of Fe concentration.............................................................46

Figure 10 Absorbance as a function of Mn concentration..........................................................47

Figure 11 Perkin-Elmer model 4100ZL Zeeman graphite furnace atomic absorption
spectrometer used for arsenic analysis........................................................................48

Figure 12 Calibration curve for arsenic analysis........................................................................50

Figure 13 Residual arsenic concentrations achieved with an initial Fe/As ratio of 100 as a
function of pH.............................................................................................................53

Figure 14 Typical flux rate of DI water with Supor®200 membrane at 10 psi (blank test).......55

Figure 15 Typical permeability of DI water with Supor®200 membrane at 10 psi (blank test).55

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